/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.hbase.regionserver;

import java.io.IOException;
import java.util.List;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.CellComparator;
import org.apache.hadoop.hbase.regionserver.compactions.CompactionContext;
import org.apache.hadoop.hbase.regionserver.compactions.CompactionPolicy;
import org.apache.hadoop.hbase.regionserver.compactions.Compactor;
import org.apache.hadoop.hbase.util.ReflectionUtils;
import org.apache.yetus.audience.InterfaceAudience;

/**
 * StoreEngine is a factory that can create the objects necessary for HStore to operate.
 * Since not all compaction policies, compactors and store file managers are compatible,
 * they are tied together and replaced together via StoreEngine-s.
 */
@InterfaceAudience.Private
public abstract class StoreEngine<SF extends StoreFlusher, CP extends CompactionPolicy, C extends Compactor, SFM extends StoreFileManager> {
    protected SF storeFlusher;
    protected CP compactionPolicy;
    protected C compactor;
    protected SFM storeFileManager;

    /**
     * The name of the configuration parameter that specifies the class of
     * a store engine that is used to manage and compact HBase store files.
     */
    public static final String STORE_ENGINE_CLASS_KEY = "hbase.hstore.engine.class";

    /********
     * TODO_MA 马中华 https://blog.csdn.net/zhongqi2513
     *   注释：
     */
    private static final Class<? extends StoreEngine<?, ?, ?, ?>> DEFAULT_STORE_ENGINE_CLASS = DefaultStoreEngine.class;

    /**
     * @return Compaction policy to use.
     */
    public CompactionPolicy getCompactionPolicy() {
        return this.compactionPolicy;
    }

    /**
     * @return Compactor to use.
     */
    public Compactor getCompactor() {
        return this.compactor;
    }

    /**
     * @return Store file manager to use.
     */
    public StoreFileManager getStoreFileManager() {
        return this.storeFileManager;
    }

    /**
     * @return Store flusher to use.
     */
    public StoreFlusher getStoreFlusher() {
        return this.storeFlusher;
    }

    /**
     * @param filesCompacting Files currently compacting
     * @return whether a compaction selection is possible
     */
    public abstract boolean needsCompaction(List<HStoreFile> filesCompacting);

    /**
     * Creates an instance of a compaction context specific to this engine.
     * Doesn't actually select or start a compaction. See CompactionContext class comment.
     *
     * @return New CompactionContext object.
     */
    public abstract CompactionContext createCompaction() throws IOException;

    /**
     * Create the StoreEngine's components.
     */
    protected abstract void createComponents(Configuration conf, HStore store, CellComparator cellComparator) throws IOException;

    private void createComponentsOnce(Configuration conf, HStore store, CellComparator cellComparator) throws IOException {
        assert compactor == null && compactionPolicy == null && storeFileManager == null && storeFlusher == null;
        createComponents(conf, store, cellComparator);
        assert compactor != null && compactionPolicy != null && storeFileManager != null && storeFlusher != null;
    }

    /**
     * Create the StoreEngine configured for the given Store.
     *
     * @param store          The store. An unfortunate dependency needed due to it
     *                       being passed to coprocessors via the compactor.
     * @param conf           Store configuration.
     * @param cellComparator CellComparator for storeFileManager.
     * @return StoreEngine to use.
     */
    public static StoreEngine<?, ?, ?, ?> create(HStore store, Configuration conf, CellComparator cellComparator) throws IOException {

        /********
         * TODO_MA 马中华 https://blog.csdn.net/zhongqi2513
         *   注释：
         */
        String className = conf.get(STORE_ENGINE_CLASS_KEY, DEFAULT_STORE_ENGINE_CLASS.getName());
        try {
            StoreEngine<?, ?, ?, ?> se = ReflectionUtils.instantiateWithCustomCtor(className, new Class[]{}, new Object[]{});
            se.createComponentsOnce(conf, store, cellComparator);
            return se;
        } catch(Exception e) {
            throw new IOException("Unable to load configured store engine '" + className + "'", e);
        }
    }
}
